Day 1.
Assess the damage:
Removed the covers - All PCBs present (this sounds obvious but many items bought on Ebay as non working with “one careful lady owner” are actually “cut & shut” items. These are a collection of non working system components put together to get rid of the surplus of spare duff boards that dealers collect over the years).
Check for evidence of internal fires and component abuse – I did see that two of the ASIC chips had been off at some point, the dodgy soldering and excessive flux around the chips was a dead giveaway, general board interconnections were intact– All seemed to check out ok.
‘Bite the bullet’ – Apply mains power, wait for the smoke etc – No smoke, no display, not much of anything really, which is actually a good sign, there is nothing like a smoking, spitting piece of electrical gear to wake you up.
Check the PSU outputs – The +12v rail present, -12V rail present, 5v rail dead – a good result and it is a linear PSU as well which is nice and easy to work with, especially as I have the schematics, which is unusual for me as I am told that only ‘wimps’ normally need a circuit diagram to fix things.
Remove PSU – the 5V regulator is hanging off the PCB, probably due to the keyboard being dropped at some point.
Re-attach the regulator and reinforce the solder connection to the PCB.
To save on fuses, I simulate the power transformer inputs to the board with bench power supplies, paying close attention to current limit settings, there is no point watching the PCB fry when you can limit the damage.
5 volt rails now come up ok and I can add a suitable load. The Oscilloscope monitoring the rails shows a clean supply without any oscillation or spurious signals.
Now it is time to disconnect the bench power supplies and try the unit with its mains transformer. Doing this initially via a mains isolating transformer is always a good move.
All rails come up ok, declare the power supply good to use.
Reinstall the power supply and power up the keyboard (still via the isolating transformer). This time the processor board kicks in and the LCD on the front panel displays the currently selected patch. This looks promising…. celebrate with a coffee.
Would the keyboard produce sound?
Initially it didn’t, the audio faders were so corroded that no amount of audio would go through them. A few squirts of switch cleaner brought some life back and the current 80’s “DigitalNativeDance” patch was
crackling though the headphones. It has a good chance of living, time to move on.